Is there a way to find out more info, such as who the user is (username), the IP of that user, and machine name? The Terminal app can show some info by using w or who, but only another username is shown. Can more info be obtained by using another command line or another app?

As far as I know, w and who will report users who are logged in via ssh. But if they are sharing files (or other resources?) on your computer, you won't find them that way.
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Harald Hanche-OlsenJul 8 '12 at 22:04